Recent evidence suggests several morphological, biochemical, and connectional similarities between the basal ganglia and the central amygdaloid nucleus, bed nucleus of the stria terminalis, and substantia innominata (hence referred to as the allostriatopallidal system). The latter system is involved in complex visceromotor behaviors such as conditioned emotional responses. Although the thalamic relations of the striatopallidal system are well-known, the thalamic relations of the allostriatopallidal system are obscure, though it is known that the midline thalamus is involved. The goal of this project is to understand the relationship of the allostriatopallidal system with the thalamus. These thalamic connections could mediate especially elaborate visceromotor responses which, in primates, might play a role in guiding social behavior. Like the allostriatopallidum, the midline thalamic nuclei contain a wide variety of peptidergic fibers. Close examination of the distribution of these fibers reveals 3 different topographies in the dorsal midline and intralaminar nuclei, which would match the topography of the origin of projections to allostriatum and ventral striatum. To understand the relationship between the thalamus and the allostriatopallidal and ventral striatopallidal systems, retrograde fluorescent tracers (including fluorescent microspheres) and Phaseolus vulgaris leucoagglutinin will be injected into midline thalamic nuclei and ventral and allostriatopallidal structures. Injections of retrograde tracers into the ventral and allostriatal systems will be combined with peptide immunofluorescence to understand the relationship between the origin of thalamic projections to allostriatum and ventral striatum and the peptidergic innervation of the midline thalamus. To determine the origin of peptidergic fibers to the midline thalamus, injections of retrograde tracers into the midline thalamus will be combined with immunofluorescence. These experiments will help establish whether the allostriatopallidal system is indeed parallel to the better understood dorsal and ventral striatopallidal systems and if the thalamic parts of these circuits are influenced by parallel neuromodulatory influences.